How will the effects of global warming affect plant species? Which species will survive, and which will die out as the result of climate change and changing rainfall and temperature patterns?
Scientists need long-range data to make accurate predictions. Armed with 25 years of records, researchers can look back to see which plant species have increased in number and which have decreased. With this information, they can determine which populations responded well to increases in temperature, rainfall and other climatic changes.
In determining the likelihood of species success, researchers consider other factors as well. For example, does the ability of a desert plant species to tolerate water stress and high temperatures guarantee its success as climate changes increase? Not necessarily, says Dr. Kent Bradford of the Seed Biotechnology Center at the University of California, Davis (UC Davis). As it turns out, a species’ ability to tolerate water stress and high temperatures only affects how well the plants in that species will grow. In order for a species to survive, the plants must also have high reproductive success.
Changes in reproductive success for annual plants are determined by how many seeds a plant can make, and how many of those seeds will be successful the next year. As researchers explore plant species ecology more deeply, they see more evidence that germination is a critical component of species survival. Bradford describes germination time as “the big crunch time for plants.”
Most plants produce many more seeds than will grow to maturity. In one growing season, it may not seem like a big deal if a plant’s seedling success rate varies by a few percent over the previous season. However, that same few percent difference can add up to a lot of plants over time. Over several years, the success rates accumulate and can have a big impact on the stability of the species. This is particularly relevant for seeds in natural environments.
Many highly domesticated crops, where the seed is the main product, are quite reliable. High germination and seedling survival result from precision planting and optimal management of soil and water. These seeds have largely lost the dormancy mechanisms that helped them schedule their germination for the optimal environmental conditions for seedling survival.
In contrast, many vegetable seeds, such as lettuce or carrot, still behave in some ways like wild species. When seeds are produced in different locations or different conditions, they can behave quite differently; they can be more dormant or less, more vigorous or less, and so on. If vegetable crop seeds behaved more like bean, wheat or corn seeds, then vegetable growers could plan for and count on more successful stand establishment.
Bradford and his colleagues at UC Davis strive to make vegetable seeds more reliable so growers will be able to count on yields, even in an unpredictable climate.
“In vegetables, the whole seed cycle is very distinct from production of the commodity. In many cases it’s a two-year process to make seed. It’s a really different type of domestication. You have highly domesticated vegetative parts, like cabbage heads, [but] once it flowers, you have a lot of traits you’d really like to get rid of,” says the veteran researcher. “We’re focusing on trying to domesticate or make those seeds more consistent, more uniform, so when the growers get the seed, they can rely on it.”
Currently, growers often overplant in order to get desired plant populations. To get a plant every foot, one might plant seeds every 2 inches. Some seeds come up and some don’t, and the plants might not be properly spaced, so the grower has to thin them out.
“In the perfect world, we would plant one seed and get one plant,” says Bradford. As seed gets more expensive, Bradford has noticed a trend among growers to using more transplants. “When seed gets really expensive, you stop throwing it into the ground and hoping; you start growing transplants and transplanting the seedlings. You see this tendency with tomatoes. Hybrid tomato seeds have really taken off, even in the processing world. More and more transplants are being used because it’s a more efficient way to use the more expensive seed.”
At the same time, growing transplants puts more pressure on seed quality. Unless the seedlings in flats all come up at the same time and are extremely uniform, the whole transplanting process becomes inefficient.
The research taking place at UC Davis’ Seed Biotechnology Center has improved scientists’ understanding of how seeds work and what contributes to quality. As they learn more, the researchers share the information with seed companies, who in turn use the information to develop new varieties of vegetables.
“We’re not making varieties, we’re making tools that make the breeding work easier for seed companies. We’re finding the genetic markers and handing them over to breeders who use them to develop varieties that are released commercially,” Bradford explains.
The researcher looks forward to exploring interesting developments in seed biology. Just as wild species need to adjust their seed characteristics in order to adapt to changing environments, crop plant breeders can adjust seed traits to better fit into cropping systems that must adapt to climate change. Successful germination and stand establishment are the critical starting points for crop production, so attention to seed quality along with other varietal characteristics is important in the breeding process.
The author is a freelance writer based in Massachusetts and a monthly contributor to Growing.